1. Field of the Invention
The present invention relates to a method and related communication device utilized in a wireless communications system and more particular to a method and related communication device of performing data transmission corresponding to semi-persistent resources.
2. Description of the Prior Art
A long-term evolution (LTE) system, initiated by the third generation partnership project (3GPP), is now being regarded as a new radio interface and radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, an evolved universal terrestrial radio access network (E-UTRAN) includes a plurality of evolved Node-Bs (eNBs) and communicates with a plurality of mobile stations, also referred as user equipments (UEs). The E-UTRAN and the eNBs are seen as part of the network side.
Semi-persistent scheduling (SPS) is introduced to the LTE system for both uplink and downlink scheduling for reducing overhead of control information sent on a physical downlink control channel (PDCCH). Take downlink transmission for example. When semi-persistent downlink resources are configured, the UE is allowed to periodically receive data block sent on a downlink shared channel (DSCH) without the control information of the PDCCH that shall be sent by the network. The period is configured by a certain amount of subframes.
The control information involved with SPS includes a C-RNTI (cell radio network temporary identifier) and an SPS C-RNTI. As well known, the C-RNTI provides the UE with a unique UE identification at the cell level identifying RRC (radio resource control) Connection and used for scheduling. The SPS C-RNTI is a UE specific identity assigned by RRC for activation or modification of semi-persistent resources. The E-UTRAN activates or modifies the semi-persistent resources by sending the SPS C-RNTI and a NDI (New Data Indicator)=0 on the PDCCH. Resource assignment for retransmission is addressed by the SPS C-RNTI and the NDI=1 on the PDCCH.
The related semi-persistent downlink scheduling operation of the UE is described below. (1) In the sub-frames where the UE has semi-persistent downlink resources, if the UE cannot find its C-RNTI on the PDCCH(s), a downlink transmission according to the semi-persistent allocation that the UE has been assigned in a TTI (Transmission Time Interval) is assumed. (2) Otherwise, in the sub-frames where the UE has the semi-persistent downlink resources, if the UE finds its C-RNTI on the PDCCH(s), the PDCCH allocation overrides the semi-persistent allocation for that TTI, and the UE does not decode the semi-persistent resources.
The related semi-persistent uplink scheduling operation of the UE is described below. (3) In the sub-frames where the UE has semi-persistent uplink resources, if the UE cannot find its C-RNTI on the PDCCH(s), an uplink transmission according to the semi-persistent allocation that the UE has been assigned in the TTI can be made. (4) Otherwise, in the sub-frames where the UE has semi-persistent uplink resource, if the UE finds its C-RNTI on the PDCCH(s), the PDCCH allocation overrides the persistent allocation for that TTI, and the transmission of the UE follows the PDCCH allocation instead of the semi-persistent allocation. (5) Retransmissions are either implicitly allocated in which case the UE uses the semi-persistent uplink allocation, or explicitly allocated via PDCCH(s) in which case the UE does not follow the semi-persistent allocation.
For uplink and downlink, the UE determines whether to use PDCCH allocation or semi-persistent allocation only according to the C-RNTI sent on PDCCH. However, the C-RNTI is unable to indicate the UE that an uplink or a downlink grant is accompanied. C-RNTI allocation without the related grant allocation can cause radio resource misusing in related subframes, thereby degrading system performance.
In addition, an SI-RNTI (System Information RNTI) indicating existence of broadcast system information may be allocated and overlapped the C-RNTI. Therefore, the following issues are found according to the abovementioned downlink and uplink scheduling operations.
Issue 1 is described in this paragraph. In a sub-frame where a UE 1 has semi-persistent downlink resources, if an eNB allocates this sub-frame to another UE (UE 2) for dynamic scheduling, the UE 1 cannot find its C-RNTI but still decodes this sub-frame with semi-persistent allocation. However, the UE 1 cannot decode it successfully according to (1) and thereby reports a NACK (negative acknowledgement) to the eNB. This makes interference to UE 2 transmission for ACKs (positive acknowledgements) or NACKs.
Issue 2 is described in this paragraph. In a sub-frame where a UE has semi-persistent downlink resources, if an eNB allocates this sub-frame to transmit system information, the UE cannot find its C-RNTI but finds an SI-RNTI. However, the UE still decodes this sub-frame with semi-persistent allocation according to (1). Therefore, the UE cannot decode the system information successfully.
Issue 3 is described in this paragraph. In a sub-frame where a UE has semi-persistent downlink resources, if the UE finds its C-RNTI on PDCCH(s) for uplink resource assignment for dynamic scheduling, the UE does not decode the semi-persistent resources and try to decode the PDSCH with the PDCCH allocation according to (2). However, the PDCCH allocation is used for uplink dynamic scheduling resources.
Issue 4 is described in this paragraph. In a sub-frame where a UE 1 has semi-persistent uplink resources, if an eNB allocates this sub-frame to another UE (UE 2) for dynamic scheduling, the UE 1 cannot find its C-RNTI but still transmits uplink data with the semi-persistent allocation according to (3). This makes interference to UE 2 data transmission.
Issue 5 is described in this paragraph. In a sub-frame where a UE has semi-persistent uplink resources, if the UE finds its C-RNTI on PDCCH(s) for downlink resource assignment for dynamic scheduling, the UE transmission follows the PDCCH allocation according to (4). However, the PDCCH allocation is for downlink dynamic scheduling resources.
Issue 6 is described in this paragraph. In a sub-frame where a UE 1 has semi-persistent uplink resources for retransmission, if an eNB allocates this sub-frame to a UE 2 for dynamic scheduling, the UE 1 cannot find its C-RNTI but still transmits uplink data with the semi-persistent allocation for retransmission according to (5). This makes interference to UE 2 data transmission.